A circuit for converting first and second differential input signals into an output signal is provided with a first differential input stage comprising first and second inputs for receiving the first differential input signal and comprising first and second outputs and with a second differential input stage comprising third and fourth inputs for receiving the second differential input signal and comprising third and fourth outputs and with an output stage comprising a first terminal connected to the first output that is further connected to the third output and comprising a second terminal connected to the second output that is further connected to the fourth output and comprising a third terminal for providing the output signal, to avoid complex operational amplifiers. The differential input stages comprise two pairs of transistors and the output stage comprises a current mirror with a third pair of transistors. A regulator comprises the circuit and a modulator stage for in response to the output signal modulating a voltage supply signal.